8
S
plitting
C
Article
by:
Harry Bickerstaffe
2nd year medical student
B
rain
&
The
onsciousness
9
Editor’s
Note:
Harry knocks it out of
the park again, with an
enthralling article, on the
interesting concept of
consciousness, relating to
evidence and cases of corpus
collosotomy, and how this
affects a person. Amazing
stuff Harry, thank you!!
The split brain phenomenon drives us to wonder whether
an area that has no effect on “my” consciousness is in
fact an area that houses a different consciousness
Splitting the Brain & Consciousness
Sphincter 80:2
December 2016
You are going to the doctor to
have your brain cut in half. You
probably have epilepsy, very bad
epilepsy because you’re saying
goodbye to the 200 million axons
of your corpus callosum as a last
resort.
The easiest
experiments with
split brain patients
exploit the fact
that visual fields
are interpreted
by the opposite
brain hemisphere
— remember that nearly all body
muscles are controlled by the
opposite side of the brain (things
get confusing very quickly if we
forget that). Showing an image to
the right eye means only the left
hemisphere will see it, in a split
brain patient.
Reference 3. Cleverly the word appears for less time than it takes for saccadic eye movement, ensuring
only one hemisphere will see the word. In this experiment images are used, words have also been used
as understanding individual words is not confined to one hemisphere.
by right hemisphere) will pick up
the hammer. To make this trickier
the objects are hidden behind a
screen. The patient chooses the
right object from amongst 20
others. When asked what object
they are holding behind the
screen the patient’s talkative left
hemisphere cannot say. When the
object is brought out from
behind the screen and
the patient is again asked
why she chose this object
out of 20 possibilities the
answer is confabulated, or
simply not known. This is
peculiar.
Back to
cutting your
brain in half!
The diagram above3 shows a
classic experiment: the written
explanation is a bit wordy, but
worth it. A split brain patient
again sees words flash infront of
her. Each word is only seen by one
side of the brain. Every word is an
object. When the left eye, i.e. the
right hemisphere, sees the word
“hammer” and the patient is asked
what she sees, she says “nothing”,
as the left hemisphere (responsible
for speech) really does see nothing.
However, when asked to pick up
the object that they didn’t see the
word for, the left hand (controlled
Back to cutting your brain in half.
There are no pain receptors in
the brain and hemispherectomies
have been performed without
loss of consciousness, so we can
cut you when you’re awake, too.
What would
happen to your
sense of “self”
the moment
your brain is
split? Does your
subjectivity
collapse
into a single
hemisphere, or
do you disappear
and become replaced by two new
consciousnesses? You cannot be
on both sides of the great divide.
to each eye only went to one
hemisphere), it was discovered
that only simple learning acquired
through one eye could transfer
to the other hemisphere. Given
the vast amount of data in each
hemisphere of human
brains, it seems likely
that a normal brain
will be functionally
split in some ways.
Two hundred
million nerve fibres
seem insufficient
to integrate the
simultaneous activity
of some 20 billion
neurons in the cerebral cortex,
each of which makes thousands of
connections.
It is perhaps tempting to think that
“you” will always fall into the left
hemisphere, that you will be the
one that converses with your loved
ones, and the researchers. Yet who
will shake their hand with your
left hand, recognise their facial
expressions and tone of voice?
The straightforward answer is that
consciousness is divisible. Just as
two different brains do not share
consciousness, the consciousness
of a single brain does not need to
be shared when the connections
are cut. And if there were to be
a way of linking two brains with
an artificial corpus callosum,
we should expect that what had
been two distinct persons would
be unified in the only sense that
consciousness is ever unified, as
a single point of view, and unified
in the only sense that minds are
ever unified, by virtue of common
contents and functional abilities.7
The idea that you may not be the
only consciousness point of view
reading this text is flabbergasting.
I cannot even feign knowing
enough to guide us on a journey
down the rabbit hole that is
the theories of consciousness.
Nevertheless, I want to highlight a
few unusual points.
“The simple
truth is that
your mind can
be split with
a surgeon’s
knife.”
Now some astonishing and subtle
things are going to happen - as
your brain and mind are split.
Firstly, your epilepsy will hopefully
have improved. Apart from that,
you appear to have remarkable
‘social ordinariness’ — how
disappointing for the researchers
hoping to probe you.1 However,
when then asking one young split
brain patient2 what he wanted to
be when he grew up: his left brain
- where language control lies for
most people - verbally responded
“a draftsman” whereas his right
brain used his left hand to write
out “racing driver”. Maybe not so
normal after all.
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impossible for normal people. In
the acute phase after surgery the
patients’ left and right hands
can be seen engaging in a tug
of war over an object or even
sabotaging each other’ s work! The
left hemisphere (with which you
would converse) can explain their
operation and their condition,
yet the left hemisphere remains
naive as to the experiences of the
right hemisphere. Years after
surgery the left hemisphere may
still express frustration when
the right hemisphere responds
to researcher’s instructions.5 To
ask the left hemisphere what it
is like not to know what the right
hemisphere is thinking is rather
like asking a normal person what
it is like not to know what another
person is thinking.
In a different experiment a split
brain patient watched a series
of picture slides, only seen in
the left visual field, so the right
hemisphere. At one point a nude
photo appeared
The most startling
What would
in the slides,
realisation is that we have
the patient was
happen to your every reason to believe
asked what she
the right hemisphere is
sense of “self” conscious. In fact it is
saw, she said
the moment your easier to establish the
“nothing”, but
then started to
consciousness of the
brain is split?
laugh. When
isolated right hemisphere
asked what
than most toddlers. In
was funny she
even more dramatic
told the researcher she didn’t
operations patients have had their
know, saying that maybe it
left hemisphere removed, leaving
was something to do with the
only their right — we rightly think
machine.4
of them as conscious. Patients
with only a right hemisphere can
The apparent liberation of the
live fruitful lives.6 How then could
right brain can be seen when split
the presence of a separate left
brain patients draw two different
hemisphere rob the other side of
figures at the same time, a task
its consciousness?
Sphincter magazine | volume 80 issue 2 | Winter 2016 edition
Back to cutting your brain in half.
There are no pain receptors in
the brain and hemispherectomies
have been performed without
loss of consciousness, so we
can cut you when you’re awake,
too. What would happen to your
sense of “self” the moment
your brain is split? Does your
subjectivity collapse into a single
hemisphere, or do you disappear
and become replaced by two new
consciousnesses? You cannot be
on both sides of the great divide.
You let me cut your brain in half,
so now you can electrocute mine
a bit. You expose my cortex and
stimulate various parts with a
microelectrode to see what effects
each part has on my consciousness.
What could either of us make of an
area that, when stimulated has no
effect on “my” consciousness? I
may say nothing happened.
The split brain phenomenon
drives us to wonder whether
an area that has no effect on
“my” consciousness is in fact
an area that houses a different
consciousness (possibly among
many different consciousnesses
in my brain)— like the right
hemisphere being unknown to
the articulate left, in split brain
patients. Here lies a perhaps
insurmountable challenge in
studying consciousness. As long
as we must correlate first person
changes with changes in the brain
we may fail to take into account
the aspects of consciousness which
are not functionally articulate, yet
may be conscious.
The uncanny point about
consciousness can be made far
more eloquently by neuroscientist
and philosopher, Sam Harris,
“there is nothing about the
brain, studied at any scale, that
even suggests that it might
harbor consciousness — apart
from the fact the we experience
consciousness directly and have
correlated many of its contents, or
lack thereof, with processes in our
brains.”7
As for unconscious thinking, I
have completely ignored it in this
article — in an effort to reduce
the number of embarrassing
mistakes. However, studying the
boundary between conscious and
unconscious thinking has been
Thank you to:
The simple truth is that your mind
can be split with a surgeon’s knife.
What if my brain is not cut in half?
Roger Sperry won the 1981 Nobel
Prize for his work with split
brain patients on brain function
asymmetry, which was briefly
alluded to above. However
some of his work in the 1950s
demonstrated that our brains
may already be split to some
degree. After cutting the optic
chiasma in cats (so that inputs
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getting increasingly precise and a
good place to look may be Daniel
Kahneman’s Nobel Prize winning
theories of two systems in making
decisions.8 Another eery area is the
disorder of “blind sight”, where
you think you are completely blind
— yet when asked to guess what is
in front of you, you can give a near
perfect description.9
The one fact we can (try to) rejoice
in is that even ridiculous-sounding
procedures can lead to remarkable
discoveries.
Notes:
1. Bayne, T. 2008. “The Unity of
Consciousness and the Split-Brain
Syndrome”,
The Journal of Philosophy, 105(6),
277-300.
2. This patient was slightly strange
as he expressed language ability in
both hemispheres.
3. Wolman, D. 2012. “The Split
Brain: A Tale of Two Halves”,
Nature 483, 260–263. Diagram
adapted, using https://neuwritesd.
org/2015/08/27/two-brains-in-onehead-the-story-of-the-split-brainphenomenon/ to depict a slightly
stranger experiment.
4. Page 704-710 of F. M. Bear’s
“Neuroscience: Exploring the Brain”,
International Edition, 4th edition
5. Gazzaniga, M. S., Bogen, J. E.,
& Sperry, R. W. (1962). “some
functional effects of sectioning the
cerebral commissures in man”,
Proceedings of the National Academy
of Sciences of the United States of
America, 48(10), 1765–1769.
6. Hemispherectomy patients’
intelligence often goes up, likely
since their other hemisphere is
causing less seizure problems. In
a similar example, Locked-In
Syndrome can render a person
devoid of the complex behaviours
we correlate with consciousness.
Jean-Dominique Bauby had
Locked-In Syndrome and could only
communicate via blinking his left
eyelid, but no one would doubt his
consciousness — especially when
reading his haunting recount of his
experiences in his new body and in
hospital (“The Diving Bell and The
Butterfly”, 1997).
7. Chapter 2: The Mystery of
Consciousness of Sam Harris’s
“Waking Up”, 2014
8. Daniel Kahneman’s “Thinking,
Fast and Slow”, 2012
9. Weiskrantz, L. (2009), ‘Is
blindsight just degraded normal
vision?’, Experimental Brain
Research 192(3), 413--416.
Sphincter magazine | volume 80 issue 2 | Winter 2016 edition